I would say that the 2600 would not deliver the same performance as the 3500 - it will deliver superior performance. The 2600 has a max 450Mbps data rate, whereas the 3500 has a max data rate of 300Mbps. The 2600 is a 3x4:3 access point vs. the 2x3:2 3500. You will get a better piece of hardware with the 2600, and if you can get it for less that is just icing on the cake.
Answer
I would say that the 2600 would not deliver the same performance as the 3500 - it will deliver superior performance. The 2600 has a max 450Mbps data rate, whereas the 3500 has a max data rate of 300Mbps. The 2600 is a 3x4:3 access point vs. the 2x3:2 3500. You will get a better piece of hardware with the 2600, and if you can get it for less that is just icing on the cake.